This invention pertains to a landing assistance system for aircraft. More particularly, the present invention is related to landing assistance systems which assist control of an aircraft, either manually or by autopilot, for piloting an aircraft along a predetermined glide path associated with a particular landing strip or runway. The invention is particularly directed to an aircraft landing system wherein the precise position of the aircraft and its deviation from a prescribed glide path is determined in a relatively simple yet highly accurate manner.
Today's commercial aircraft commonly incorporate MLS (Microwave Landing System) or ILS (Instrument Landing System). These landing assistance systems are particularly important during those aircraft landings under adverse visibility conditions. Such systems, therefore, assist the pilot in enhancing safe landings.
In ILS and MLS type landing assistance systems, associated with each landing strip is the employment of electromagnetic wave generating equipment for radiating a plurality of electromagnetic wave beams having electromagnetic characteristics which define a glide path for a specific landing strip. The aircraft includes appropriate signal receiving equipment depending upon the system employed for determining the position of the aircraft relative to the glide path as defined by the electromagnetic wave generating equipment. In turn, onboard aircraft signal processing equipment may be utilized to provide data to the human pilot through landing indicating equipment, or else be given to an automatic pilot control system, referred to as an autopilot.
Another type of landing assistance system using satellite positioning data is shown and described in U.S. Pat. No. 4,894,655, issued to J. C. Jognet et al. The landing assistance system described therein incorporates a differential GPS satellite positioning system well established and known in the prior art which incorporates a fixed ground station having a known reference position. The fixed ground station is located in the vicinity of a landing strip. The fixed ground station contains a receiver for receiving satellite signal data from a plurality of satellites from which pseudo range data and pseudo range rate data, herein referred to as satellite data, are derived therefrom. From the satellite range data, a measured or estimated global position of the ground station receiver may be determined. In differential GPS systems, the ground station further includes a computing device for comparing the theoretical range between the known reference global position of the ground station and the position of the satellites to derive correction data representative of the error, if any, in the pseudo range and pseudo range rate data. In turn, other remote GPS stations can correct their calculated position by correcting the satellite data with use of the correction data to determine a "corrected" global position of the remote GPS station. The fixed ground station also includes a data link signal transmitter, e.g., an RF transmitter, for transmitting on a MLS radio channel GPS correction data, landing strip data associated with the landing strip including the magnetic alignment, the coordinates of the desired approach end of the landing strip, and the identity of the landing strip. Further, as part of the landing assistance system, the aircraft incorporates an onboard receiver for determining its calculated position based on substantially the same GPS-like data. Secondly, the onboard equipment also includes a receiver for receiving the correction data and the aforementioned landing strip data. In turn, a conventional onboard computer determines the landing guidance data which may be given to the human pilot by landing indicating equipment, or utilized as inputs to an autopilot.
A disadvantage of the aforementioned GPS aided landing system is the inherent ambiguity in the magnetic alignment heading of the runway as well as a clear definition of glide path.